The present invention relates to a communication system for processing outgoing and incoming data. More particularly the invention relates to a baseband unit for handling packets comprising a header and payload.
Although the present invention is applicable in a broad variety of communication systems it will be described with the focus put on an application to a short-range radio communication system that conforms to the Bluetooth baseband specification, as can be found in “Specification of the Bluetooth System”, Version 1.0 B, Bluetooth Special Interest Group (SIG), Dec. 1, 1999.
The intensified wish to connect a wide range of computing and telecommunications devices easily and simply, without the need to buy, carry, or connect cables, has been realized by several companies. The Bluetooth Special Interest Group (SIG) and the IEEE Wireless Personal Area Network (WPAN) standardization group 802.15 are working on a specification of a short-range radio communication system for enabling wireless ad-hoc connectivity between portable and/or fixed electronic consumer products such as computers, cellular phones, printers, and digital cameras. This communication system can manage within a small local area up to three synchronous connection-oriented (SCO) links mainly for speech transmission at a rate of 64 kbit/s, and up to seven asynchronous connectionless (ACL) links supporting symmetric or asymmetric data transfers at a maximum rate of 433.9 and 723.2 kbit/s, respectively. The radio subsystem is operated in the globally available unlicensed industrial, scientific, and medical (ISM) frequency band at 2.4 GHz, covers distances of up to 10 meters with a transmission power of less than 1 mW, and applies frequency hopping in conjunction with a time-division multiple access (TDMA) scheme for transmitting data at a symbol rate of 1 Mbit/s over the air. Crucial for the acceptance of this new communication technology in commercial products is the design of a low-power, small-sized, low-cost radio subsystem that can be embedded in existing and future, portable and fixed electronic consumer devices.
Known architectures for Bluetooth transceivers use several modules within a signal processing chain. Thereby, at least one signal processing chain is used for transmitting and at least another one for receiving packets. For example, in the transmitter chain, user synchronous, user asynchronous, or user isochronous data are sent via corresponding logical channels to transmit buffers for synchronous connection-oriented (SCO) links and buffers for asynchronous connection-less (ACL) links. Control information stemming from a link manager protocol, as described in the Specification of the Bluetooth System, can also be fed to the ACL buffers. The stored information in each of the multiple ACL and SCO buffers represents the payload to be transmitted over the link. Before its transmission, the payload is processed by appending cyclic redundancy check (CRC) bits, ciphering, whitening, and optionally encoding with a rate 1/3 or 2/3 forward error correction (FEC) code. The latter can be achieved by a CRC generator, an encryption module, a whitening filter, and an FEC encoding module. In parallel, the packet header is assembled by a link controller and stored in a transmit header register. The header is processed by appending error check (HEC) bits from a HEC generator, whitened with a respective filter, and encoded with a rate 1/3 FEC code with a respective FEC encoding module. A radio frame is obtained by first concatenating the filtered and coded header and payload information, and then preceding the resulting bit string with an access code. Finally, the radio frame is forwarded to an analog radio frontend for its transmission at a frequency f(n). The value of f(n) is provided by a hopping frequency selection block.
A corresponding receiver chain might have the following features. When an access code correlator detects the arrival of a radio frame at a frequency f(n), a trigger event starts the processing in the receiver chain. The header information is extracted from the received frame, decoded with an FEC decoder, dewhitened with a dewhitening filter, checked by a HEC checking module, and stored in a receive header register. When the HEC check is successful, the receiver can start decoding, dewhitening, deciphering, and CRC checking the payload information with an FEC decoder, dewhitening filter, decryption module and a CRC checking module, respectively. When the CRC check is successful, the packet is stored in either a receive SCO buffer or ACL buffer depending on the received packet type. From the receive buffer, the payload is carried via the logical channels for user synchronous, user asynchronous, or user isochronous data to the synchronous or asynchronous I/O port. If link manager control information has been received in the receive ACL buffer, it is forwarded to the link manager protocol.
A link controller configures, monitors, and controls the transmitter and receiver chain so that the baseband can be operated in several states.
Known disadvantages of current implementations of digital baseband systems based on rate-conversion between successive signal processing modules are the rate-conversion delay, the rate-conversion logic-overhead and power consumption.
Known buffer implementations have the disadvantage of memory inefficiency for variable length packets and a lack of addressability and allocation flexibility.
It is thus an object of the present invention to overcome the disadvantages of the state of the art and to provide a low-power, small-sized, low-cost baseband system that can be used in existing and future devices.